1. Field of the Invention
This invention relates to lance apparatus employed for either heating purposes or for ceramic welding purposes, such as providing a heating flame or conveying sand or like solid particulate material in a combustion-supporting carrier gas. In particular the invention relates to the tip configuration of a lance used alternatively to provide a flame or to effect ceramic welding. The invention also covers a process using the said lance apparatus.
2. Description of the Related Art
In ceramic welding, a mixture of solid refractory particles and solid combustible fuel particles of a metal or semi-metal such as aluminium or silicon is projected in a carrier gas stream, typically of oxygen, against a surface. The fuel particles react with oxygen in a highly exothermic manner to form a refractory oxide, sufficient heat being released against the surface to melt at least the surface of the refractory particles and form a coherent refractory mass. Such "ceramic welding" is described in Glaverbel GB patent specifications 1,330,894 and 2,170,191.
Ceramic welding can be employed for forming a refractory article, for example, a block having a particular shape, but it is most widely used for forming coatings or for repairing bricks or walls constructed of refractory oxide materials. It is particularly useful for repairing or reinforcing existing refractory furnace structures, for example, furnace walls in glassmaking or coke ovens, especially since the repair can be effected while the furnace is in operation.
In order to reach the repair zone, which may be several meters away from the operator, the lances tend to be long and to have much ancillary equipment such as flexible supply lines for the gases and particulate material. They also typically include a water-cooled jacket, with associated supply lines for the cooling water. Thus the lances can be very heavy and cumbersome to manipulate, requiring in some instances the provision of special scaffolding and associated lifting equipment to put them into the operating position.
In effecting the repair it is commonly necessary to prepare the surface to be repaired, for example to remove loose or foreign material in order to provide a sound base to which the repair mass can adhere. In some instances the repair surface has been treated by introducing a comburent gas into the zone to be repaired to burn off unwanted deposits.
Lances for use in such purposes as cleaning are long established. EP-A-0069286 relates to a lance for flame spraying a metal refining vessel including a furnace bottom cleaning device which feeds oxygen to the required point of use. Burners are also known to clean refractory surfaces.
Given the refractory nature of the base it is desirable to employ an intense cleaning flame which can if necessary quickly melt part of the surface to be repaired, leaving a fresh surface on which to effect the repair. Particularly in the case of glassmaking furnaces, a vitreous phase may be present as a residue of molten glass, as an exuded bonding phase in the refractory material or as a result of deposition of refractory dust from the vitrifiable material mixture introduced into the glass melting tank. A vitreous phase is especially likely to be found in refractory blocks at or from the level of the molten glass line in a glassmaking furnace. These blocks are typically of high quality Zac refractories.
A conventional repair of damaged or worn refractory walls within a furnace such as a glass furnace by means of first a flame treatment of the wall surface followed by spraying a ceramic welding powder mixture tends to involve much manipulation of the burner and of the ceramic welding lance. The steps of removing the burner and inserting and directing the ceramic welding lance to the flame-treated area can be difficult and time-consuming. The resultant delays, which may typically be 20 to 60 minutes, are also long enough for a vitreous phase to begin to reappear on the wall surface. Moreover the hardening effect, which creates a refractory structure which exudes less, is lost.
GB patent specification 2237803 relates to a ceramic welding nozzle which has a central bore for weld material in a gaseous fluid, such as air, and combustion means adjacent to the nozzle outlet for the injection into the gaseous fluid of a combustible fluid, such as propane, butane or acetylene. The combustion means is primarily employed to assist the weld formation by heating the weld particles and the substrate refractory. The combustible fluid mixes with the gaseous fluid from the central bore and reacts with the oxygen therein to form a heating flame in the vicinity of the repair zone. The flame can be used simply for preheating the repair surface but the defined nozzle does not lend itself to the formation of an intense flame, the combustible fluid being introduced into a gaseous fluid from the single central bore and thus being dispersed over a relatively wide area. This system does not permit and does not envisage scouring of the surface prior to the repair.
It is an object of the present invention to provide a lance which has an inbuilt capability to deliver an intense flame independently of its function for ceramic welding or like purposes.